1. Field of the Invention
The present invention relates to a method of supporting handover, and more particularly, to a method of supporting handover in a multi-mode mobile station. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for supporting handover of a multi-mode mobile station in a wireless mobile communication system.
2. Discussion of the Related Art
Generally, the object of IEEE 802.21 in progress for International Standardization of Media Independent Handover between heterogeneous networks is to enhance user's convenience for Mobile Station (MS) devices by providing seamless handover and service continuity. Basic requirements here include a MIH function, an event trigger (or event service), a command service (CS) and an information service (IS) are defined as basic requirements.
A mobile station (MS), which can also be referred to as a mobile subscriber station (MSS) or a mobile terminal, is a multi-mode node that supports at least two interface types. Here, the interface can be, for instance, a wire-line type interface such as 802.3-based Ethernet, a wireless interface type based on IEEE 802.XX, such as IEEE 802.11, IEEE 802.15, IEEE 802.16 and the like, an interface type defined by cellular standardization organization such as 3rd Generation Partnership Project (3GPP) and 3GPP2 and the like are possible.
FIG. 1 is a diagram of protocol stack architecture of a multi-modal MS. Referring to FIG. 1, the multi-modal MS comprises a Physical (PHY) layer per mode and a Medium Access Control (MAC) layer per mode. In addition, an MIH layer is placed below an Internet Protocol (IP) layer.
The MIH should be defined between IEEE802-series interfaces or between the 802-series interfaces such as the above-mentioned non-802-series interfaces defined by the cellular standardization organization such as 3GPP and 3GPP2. Moreover, a mobility supporting protocol of an upper layer such as Mobile IP and SIP (session initiation protocol) should be supported for the seamless handover service.
The MIH function is placed below the IP layer. Furthermore, the MIH function facilitates the handover process by using the input values from Layer 2 such as trigger event information and information of other networks. Moreover, the MIH function can include input values (e.g., user policy and configuration) which can affect the handover procedure. In addition, general interfaces (e.g., the Mobile IP and the SIP) are defined between Layer 3 entities and the MIH Function. These interfaces provide information associated with Layer 1 (i.e., PHY Layer) and Layer 2 (i.e., MAC Layer) as well as mobility management. The MIH function uses an event service (ES) to acquire information on lower layers and the network.
An Upper Management Entity (UPE) is located in the upper layer to monitor and control statuses of various links in the MS. Furthermore, the UPE is used to perform handover control function and device manager function. Here, the handover control function and the device manager can be independently located or can be included in the upper management entity.
In the present invention, the terms ‘upper’ and ‘higher’ are used interchangeably to describe the upper/higher management entity, upper/higher layers, and a like.
FIG. 2 illustrates a MS having a MIH function and a network having a functional entity and transmission protocol. In FIG. 2, the dotted lines represent services such as a primitive and the ES.
As illustrated in FIG. 2, for faster handover, the network layer uses the information from a link layer in order to quickly re-establish connection. The link layer event can be used to predict the user's movement and also can be used prepare for handover between the mobile terminal and the network. The trigger for handover procedure can be initiated from the PHY layer and the MAC layer. Moreover, the source of the trigger can be a local stack or a remote stack.
FIG. 3 illustrates a structure of a trigger model. An event trigger provides information related to the status of current signals, changes in status of other network, predictable changes as well as changes in the PHY layer and the MAC layer and changes in the properties of a certain network.
The event types can be classified into a PHY layer event, a MAC layer event, a management event, an L3 event, and an application event. A basic trigger event is as follows.
Link_Up notification is delivered when a Layer 2 connection is established on the specified link interface and when other upper layers can send higher layer packets. All Layer 2 activities in establishing the link connectivity are determined to be completed at this point of time. Here, the source of the Link_Up event is the Local MAC and the Remote MAC. Table 1 shows parameters of Link_Up notification.
TABLE 1NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofpreviousaccess routerMacNewAccessRouterMAC AddressMAC address ofnew accessrouterNetworkIdentifierMedia SpecificNetwork identifierfor detecting changein subnet
Link_Down notification is delivered when a Layer 2 connection is broken on the specified link and when no more packets can be sent on the specific link. Here, the source of the Link_Down event is the Local MAC. Table 2 shows parameters of Link_Down notification.
TABLE 2NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofpreviousaccess routerReasonCodeReason fordisconnected link
Link_Going_Down notification is delivered when a Layer 2 connection is expected (predicted) to go down (Link_Down) within a certain time interval. Link_Going Down event may be the indication to initiate handover procedures. Here, the source of the Link_Going_Down event is the Local MAC and the Remote MAC. Table 3 shows parameters of Link_Going_Down notification.
TABLE 3NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC addressof previousaccess routerMacNewAccessRouterMAC AddressMAC address ofnew accessrouterTimeIntervalTime in msecsPredicted time forLink_DownConfidenceLevel%Predicted specifictime forLink_DownUniqueEventIdentifierUse whenEvent_Rollbackhappens
Link_Going_Up notification is delivered when a Layer 2 connection is expected (predicted) to go up (Link_Up) within a certain time interval. Moreover, the notification is used when excessive amount of time is expanded in initializing the network. Here, the source of the Link_Going_Up event is the Local MAC and the Remote MAC. Table 4 shows parameters of Link_Going_Up notification.
TABLE 4NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC address ofnew accessrouterTimeIntervalTime in msecsPredicted time forLink_DownConfidenceLevel%Predicted specifictime forLink_DownUniqueEventIdentifierUse whenEvent_Rollbackhappens
Link_Event_Rollback indication is used in conjunction with Link_Going_Down. That is, it combines Link_Going_Up and Link_Going_Down for use. More specifically, if the link is no longer expected to go up (Link_Up) or go down (Link_Down) in the specified time interval, then a Link_Event_Rollback message is sent to the Event destination. Here, the source of the Link_Event_Rollback event is the Local MAC and the Remote MAC. Table 5 shows parameters of Link_Event_Rollback inciation.
TABLE 5NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC addressof new accessrouterUniqueEventIdentifierUse whenEvent_Rollbackhappens
Link_Available indicates a new available link. That is, Link_Available indicates the possibility that a new base station or a point of attachment (PoA) can provide better link quality than that of the PoA (which can be also referred to as an access point, a base station, or a network entity) to which the MS is connected. Here, the source of the Link_Available event is the Local MAC and the Remote MAC. Table 6 shows parameters of Link_Available.
TABLE 6NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC addressof new accessrouterMacOldAccessRouterMAC AddressMAC addressof previousaccess router
Link_Parameters_Change indicates changes in link parameters when specified threshold levels are crossed. This may include link layer parameters such as speed of the link, Quality of Service (QoS), Bit Error Rate (BER), etc. The threshold level for each such parameter can be configured through a separate command to link layer. Here, the source of the Link_Parameters_Change event is the Local MAC and the Remote MAC. Table 7 show parameters of Link_Parameters_Change.
TABLE 7NameTypeDescriptionEventSourceEVENT_LAYER_TYPESource of eventEventDestinationEVENT_LAYER_TYPETarget of eventMacMobileTerminalMAC AddressMAC addressof MSSMacAccessRouterMAC AddressMAC addressof accessrouteroldValueOfLinkParameterPrevious valueof linkparameteroldValueOfLinkParameterNew value oflink parameter
FIG. 4 illustrates a trigger when establishing a new link due to decreased quality of the current link.
An Information Service (IS) provides a framework by which a MIH Function both in the mobile terminal and in the network can discover and obtain network information within a geographical area to facilitate handovers. Here, the IS is accessible to any network. The IS includes the following information elements, such as a link access parameter, a security mechanism, a neighbor map, a location, a cost of link, and a provider and other access information.
The conventional art defines the ES, CS, and IS for the MIH. However, when the ES, CS, and IS are transmitted/received between a local stack and a remote stack based on the MIH messages, there is not a defined MIH protocol procedure, a MIH header, and a message format.